Commit message: auth: Don't crash expanding %variables when username isn't set.

This continues the auth-policy fix in
c3d3faa4f72a676e183f34be960cff13a5a725ae
CVE: CVE-2016-8652
CWE: CWE-20
Vulnerability description: The auth component in Dovecot before 2.2.27, when auth-policy is configured, allows a remote attackers to cause a denial of service (crash) by aborting authentication without setting a username.

Project: core

auth_request_get_var_expand_table_full(const struct auth_request *auth_request,
				       auth_request_escape_func_t *escape_func,
				       unsigned int *count)
{
	const unsigned int auth_count =
		N_ELEMENTS(auth_request_var_expand_static_tab);
	struct var_expand_table *tab, *ret_tab;
	const char *orig_user, *auth_user;

	if (escape_func == NULL)
		escape_func = escape_none;

	/* keep the extra fields at the beginning. the last static_tab field
	   contains the ending NULL-fields. */
	tab = ret_tab = t_malloc((*count + auth_count) * sizeof(*tab));
	memset(tab, 0, *count * sizeof(*tab));
	tab += *count;
	*count += auth_count;

	memcpy(tab, auth_request_var_expand_static_tab,
	       auth_count * sizeof(*tab));

	tab[0].value = escape_func(auth_request->user, auth_request);
	tab[1].value = escape_func(t_strcut(auth_request->user, '@'),
				   auth_request);
	tab[2].value = strchr(auth_request->user, '@');
	if (tab[2].value != NULL)
		tab[2].value = escape_func(tab[2].value+1, auth_request);
	tab[3].value = escape_func(auth_request->service, auth_request);
	/* tab[4] = we have no home dir */
	if (auth_request->local_ip.family != 0)
		tab[5].value = net_ip2addr(&auth_request->local_ip);
	if (auth_request->remote_ip.family != 0)
		tab[6].value = net_ip2addr(&auth_request->remote_ip);
	tab[7].value = dec2str(auth_request->client_pid);
	if (auth_request->mech_password != NULL) {
		tab[8].value = escape_func(auth_request->mech_password,
					   auth_request);
	}
	if (auth_request->userdb_lookup) {
		tab[9].value = auth_request->userdb == NULL ? "" :
			dec2str(auth_request->userdb->userdb->id);
	} else {
		tab[9].value = auth_request->passdb == NULL ? "" :
			dec2str(auth_request->passdb->passdb->id);
	}
	tab[10].value = auth_request->mech_name == NULL ? "" :
		escape_func(auth_request->mech_name, auth_request);
	tab[11].value = auth_request->secured ? "secured" : "";
	tab[12].value = dec2str(auth_request->local_port);
	tab[13].value = dec2str(auth_request->remote_port);
	tab[14].value = auth_request->valid_client_cert ? "valid" : "";

	if (auth_request->requested_login_user != NULL) {
		const char *login_user = auth_request->requested_login_user;

		tab[15].value = escape_func(login_user, auth_request);
		tab[16].value = escape_func(t_strcut(login_user, '@'),
					    auth_request);
		tab[17].value = strchr(login_user, '@');
		if (tab[17].value != NULL) {
			tab[17].value = escape_func(tab[17].value+1,
						    auth_request);
		}
	}
	tab[18].value = auth_request->session_id == NULL ? NULL :
		escape_func(auth_request->session_id, auth_request);
	if (auth_request->real_local_ip.family != 0)
		tab[19].value = net_ip2addr(&auth_request->real_local_ip);
	if (auth_request->real_remote_ip.family != 0)
		tab[20].value = net_ip2addr(&auth_request->real_remote_ip);
	tab[21].value = dec2str(auth_request->real_local_port);
	tab[22].value = dec2str(auth_request->real_remote_port);
	tab[23].value = strchr(auth_request->user, '@');
	if (tab[23].value != NULL) {
		tab[23].value = escape_func(t_strcut(tab[23].value+1, '@'),
					    auth_request);
	}
	tab[24].value = strrchr(auth_request->user, '@');
	if (tab[24].value != NULL)
		tab[24].value = escape_func(tab[24].value+1, auth_request);
	tab[25].value = auth_request->master_user == NULL ? NULL :
		escape_func(auth_request->master_user, auth_request);
	tab[26].value = auth_request->session_pid == (pid_t)-1 ? NULL :
		dec2str(auth_request->session_pid);

	orig_user = auth_request->original_username != NULL ?
		auth_request->original_username : auth_request->user;
	tab[27].value = escape_func(orig_user, auth_request);
	tab[28].value = escape_func(t_strcut(orig_user, '@'), auth_request);
	tab[29].value = strchr(orig_user, '@');
	if (tab[29].value != NULL)
		tab[29].value = escape_func(tab[29].value+1, auth_request);

	if (auth_request->master_user != NULL)
		auth_user = auth_request->master_user;
	else
		auth_user = orig_user;
	tab[30].value = escape_func(auth_user, auth_request);
	tab[31].value = escape_func(t_strcut(auth_user, '@'), auth_request);
	tab[32].value = strchr(auth_user, '@');
	if (tab[32].value != NULL)
		tab[32].value = escape_func(tab[32].value+1, auth_request);
	if (auth_request->local_name != NULL)
		tab[33].value = escape_func(auth_request->local_name, auth_request);
	else
		tab[33].value = "";
	return ret_tab;
}